Question : How product nos/item number/part number different from SKU?
From what I understand, SKU groups all the attributes that applies to a product and assigns a fixed number/value to it so that that one number could define a set of values within an attribute group. For example if you were to make a stock transaction, lets say item is - Mens V neck T-Shirt and item number being MN-VN-TS now suppose this product comes in two sizes(M-L) and two colours(Grey and Blue) then the item will have four SKU's one defining each combination of attributes. SZ-M-COL-GRY, SZ-L-COL-GRY, SZ-M-COL-BLU, SZ-L-COL-BLU. So the transaction will look something like :
Received 6 pcs of Item: MN-VN-TS with SKU :SZ-L-COL-GRY
Lets now say there is another item Mens Round Neck T-Shirt with same attributes item name being MN-RN-TS so transaction should appear like:
Received 6 pcs of Item: MN-RN-TS with SKU :SZ-L-COL-GRY
So what you see now is that the stock of two different products got affected but the attributes were same and hence we kept SKUs also same. This way if you need to get the stock of all grey garments you can get all the SKU's having the attribute colour with the value grey and you'll get the stock of all grey coloured garments. Where as this would not be possible if different SKU was to be used for different products having same attribute group and values. It will also make the task of new item/product creation simple which is having the same attribute set. If you keep all the SKUs different for each product then it will be a very painful job to create new SKUs for every new product you add and every possible combination of attribute values even when such combinations already have SKUs defined for some other product.
So my questions is why dose the SKU needs to be unique for each product? What purpose dose it serves by being unique?